In 1883, Nobel laureate John Strutt, a physicist and the third Baron Rayleigh, put forward a radical idea. He had been studying the mechanics of pelican flight and proposed that the birds drew energy from differentials in wind speed, allowing them to remain aloft without beating a wing. By taking advantage of this technique (since named dynamic soaring), a craft could, in theory, fly with little or no fuel for weeks, months, or even years.

For decades, work on dynamic soaring progressed slowly. Radio-control glider operators took advantage of the technique to extend their flights, but scientists didn’t know if they could apply it to larger craft. Then in 2006, a team from the U.S. Air Force and NASA flew a modified L-23 Blanik sailplane over Edwards Air Force Base, proving that a large craft is capable of dynamic soaring maneuvers.